Reeler is an autosomal mutation in mice which causes systematic malposition of neuron classes of cerebral and cerebellar cortex. This is associated with an anomaly of stratification of neuronal somata and axons which is present from the earliest period of cortical histogenesis. Studies are designed to examine the interdependence of target cell position and the organization of neural systems, the interdependence of neuronal form and the relation of cell soma to axonal strata, the limits of specificity of connections as challenged by cell malposition and, finally, the early events of cell-afferent systems interaction associated with the development of stratified cortical structures. Specimens of human developmental pathology are studied with general cell strains and the higher resolution rapid-Golgi method where opportunities present themselves. Such studies are coupled to a program of neuron morphometry designed to identify different classes of developmental pathology of individual neurons which, in turn, may aid in the identification of currently obscure disease processes affecting the developing human nervous system.